In various manufacturing processes, for example, in the manufacturing of plastic, fiberglass, wood, metal and ceramic products, the application of oils is often required to cool and/or lubricate surfaces during the forming of such products or prior to subsequent use of such products. It is often necessary to remove such oils prior to the application of a protective or decorative coating to such products. Disposal of removed oils, as well as the caustic and acidic solutions typically used to remove such oils, presents significant environmental pollution problems. Especially in industries involved in removing oils from metal surfaces, highly acidic agents, including hydrofluoric, sulfuric, phosphoric and nitric acids, are employed. For example, U.S. Pat. No. Re 32,661 by Binns discloses a method of finishing aluminum using an acidic aqueous finishing solution having a pH less than 2. Similarly, U.S. Pat. No. 3,969,135 by King discloses a composition and process for finishing aluminum using a low temperature aqueous acidic solution with a pH of less than 2. Others involved in the manufacturing of metal products employ highly caustic reagents, posing similar environmental disposal problems as those presented by the use of acidic agents. Such caustic agents include alkali metal hydroxide, hexavalent chromium, and alkali metal metasilicate (e.g., U.S. Pat. Nos. 3,951,682 by Schevey et al., 4,477,290 by Carroll et al., and 4,270,957 by Donakowski et al.). Both acidic and caustic agents must be neutralized prior to environmental discharge, thus adding to the overall costs involved in treatment operations.
Conventional acidic and caustic finishing agents are typically used in an aqueous solution. Unfortunately, water used in such finishing processes is not easily recoverable in a sufficiently pure form to permit discharge into water streams or to reuse in finishing operations. Tremendous quantities of water are polluted in conventional finishing procedures, thus necessitating the use of costly clean-up procedures to comply with increasingly strict environmental water quality regulations. Moreover, acidic and caustic finishing agents are known to react with the oils present on the surfaces being treated, thereby preventing the recovery of both uncontaminated finishing agents used in the process and uncontaminated oils removed during treatment operations. Thus, significant expenditures of time and money are required to treat or destroy the acidic, caustic and oil residues produced in such processes.
Others have proposed various recycling schemes to reduce the problems encountered in such finishing processes. For example, articles have been submerged rather than sprayed with a finishing solution to facilitate later separation of finishing solutions for potential reuse (U.S. Pat. Nos. 3,951,682 by Schevey et al., 4,498,934 by Potts, and 2,923,648 by K'burg). Such processes, however, are time consuming and therefore limit production capacity. Other methods of recycling have required addition of chemicals, such as surfactants, demulsifiers or chelating agents, to facilitate recycling of various components (e.g., U.S. Pat. No. 4,136,217 by Henley). The separation of the various components used in a finishing operation is hampered due to the presence of added chemicals rendering the reuse of various liquid streams impractical for rinsing operations.
It would therefore be desirable to provide an environmentally safe and economical method for the recycling of finishing agents, water and oils removed from surfaces during manufacturing operations. In particular, a closed loop recycling system would be highly desirable which is able to generate sufficiently uncontaminated water for reuse in such a system, and that allows for the recovery of a reusable finishing agent and reusable oils removed in the manufacturing process.